Recently, with the development of electronic industries and the advance of industrial technologies, various electronic devices are designed toward small size, light weightiness and comfortable portability. Consequently, these electronic devices can be applied to mobile business, entertainment or leisure purposes whenever or wherever the users are. For example, many imaging devices are widely used in many kinds of fields such as smart phones, wearable electronic devices or any other appropriate electronic devices. Since the imaging devices are small and portable, the users can take the imaging devices to capture images and store the images according to the users' demands. Alternatively, the images can be uploaded to the internet through mobile networks. In other words, these electronic devices not only have important commercial values but also provide more colorful lives to people.
As a consequence, the physical volume of the optical lens module applied to the imaging device is dramatically reduced. That is, the demands on the smaller thickness of the optical lens module and the smaller diameter of the optical lens module are increased correspondingly. FIG. 1 is a schematic cutaway view of a conventional optical lens module. As shown in FIG. 1, the process of assembling the optical lens module 9 is very complicated. For example, plural lenses 91 of the optical lens module 9 are installed and fixed in a barrel 93 through additional fixing structures 92. Moreover, a stray light baffle 94 is installed in the barrel 93 to prevent the stray light from passing through the lenses 91. Because of these components or structures, it is difficult to achieve miniaturization of the whole optical lens module 9. Moreover, since most lenses 91 are produced by an injection molding process, warping deformation or residual stress is possibly generated during the injection molding process. As a consequence, the difficulty of assembling the optical lens module 9 is also increased.
Moreover, for increasing the reliability of the miniature optical lens module 9, the following assembling items should be taken into consideration. Firstly, it is important to know how to increase the structural strength of the lenses 91 after the lenses 91 are assembled to the barrel 93. Secondly, it is important to know how to reduce or avoid generation of the warping deformation or residual stress of the lenses 91 during the injection molding process. After the warping deformation or residual stress is reduced or avoided, the subsequent process of assembling the optical lens module 9 will become easier, and the undesired or abrupt aberration caused by optical path variation because of the change of refractive index will be avoided. Thirdly, it is important to know how to simplify the assembled structures of the optical lens module 9 (e.g., the stray light baffle 94 or the fixing structures 92 for fixing the lenses 91 in the barrel 93) in order to simplify the assembling process of the optical lens module 9.
Nowadays, a diffractive optical lens is available in market. The diffractive optical lens is applied to the optical lens module 9 to enhance the imaging quality, for example correct aberration or eliminate chromatic dispersion. FIG. 2 is a schematic perspective view illustrating the outer appearance of a conventional diffractive optical lens. FIG. 3 is a schematic cross-sectional view illustrating the conventional diffractive optical lens of FIG. 2. As shown in FIGS. 2 and 3, the outer appearance of the diffractive optical lens is similar to the outer appearance of the general lens 91. However, the inner portion of the diffractive optical lens 8 has a diffractive structure of grating 81. The diffractive structure of grating 81 is used for modulating the light beams that pass through the diffractive optical lens 8, thereby correcting aberration or eliminating chromatic dispersion.
Generally, the diffractive optical lens 8 has a pure lens structure. That is, the entire of the diffractive optical lens 8 is an optically effective region. Consequently, in case that the diffractive optical lens 8 is applied to the miniature optical lens module, the above assembling items still need to be taken into consideration. For example, an additional fixing structure is required to install and fix the diffractive optical lens 8 in the barrel of the optical lens module.
Conventionally, since the light beams for the diffractive optical lens are in a specified wavelength range, the applications of the diffractive optical lens are limited. However, some optical products such as depth cameras, TOF cameras (time of flight cameras), infrared CCTV cameras and thermal imagers are increasingly concerned by the market, and thus the market scale of these optical products is gradually widened. Since these optical products are applied to specified wavelength ranges, the manufacturers have to pay much attention to the applications of the diffractive optical lenses.
From the above descriptions, it is an important issue to improve the structure and fabricating process of the diffractive optical lens in order to increase the available wavelength range and avoid the generation of warping deformation or residual stress during the injection molding process. Moreover, it is also important to simplify the constituents of the optical lens module by the improvement of the diffractive optical lens and increase the structural strength of the structural strength of the optical lens module after the optical lens module is assembled to the barrel. Consequently, the subsequent process of assembling the optical lens module is easier, and the overall performance is enhanced.